I came across this online. There's a condition called Normal Pressure Hydrocephalus (NPH) that causes, amongst other things, dementia that can be mistaken for Alzheimer's Disease:
In some cases the disease is treatable. Sometimes patients can make an almost complete recovery.
Everyone interested in dementia should be aware of this disease as it is one of the few conditions involving dementia for which there is, sometimes, a 'cure'. If someone with NPH is diagnosed as having AD, the consequence could be that they miss out on the possibility of successful treatment.